Numerical Aperture and Partial Coherence Optimization in Optical Li-Thography under Off-Axis Illumination
Numerical aperture NA and partial coherence sigma optimization in optical lithography is investigated for 100 nm dense lines under annular illumination and quadrupole illumination. Depth of focus (DOF) is calculated at different NA and sigma settings using PROLITH software. Based on the calculations of DOF, the NA and sigma settings are optimized by finding the values to maximize the DOF. At the optimum NA and sigma settings for 100 nm dense lines, the imaging performance is analyzed for semi-dense and isolated lines.
L. P. Guo et al., "Numerical Aperture and Partial Coherence Optimization in Optical Li-Thography under Off-Axis Illumination", Advanced Materials Research, Vols. 383-390, pp. 2437-2442, 2012